Value-added products from lignin: IsolationValue-added products from lignin: Isolation, characterization and applications

As the abundant natural macromolecular polymer on the earth, lignin fractions isolated from different pulping and pretreatment processes have received considerable attentions due to their potentials in the increasing industrial applications. However, most industrial lignin is underutilized due to their complicated, destructive and condensed structures. Meanwhile, different biorefinery processes also produce an increasing lignin with various structural characteristics and properties. In this chapter, isolation methods and structural characterization of lignin were reviewed and illustrated in a concise way. 2D-HSQC and 31P-NMR characterization of the chemical and structural features of lignin will facilitate the value-added applications of lignin obtained from different isolation processes. Specially, the lignin with well-preserved β-O-4 linkages is likely suitable for catalytic degradation of lignin. By contrast, lignin fractions with plentiful hydroxyl groups, which can be determined by 31P-NMR technique, are beneficial to the chemical modification of lignin in developing the lignin-based polymers. The lignin-based chemicals and polymeric materials can be accomplished via a series of methods and techniques. In the current biorefinery process, it is necessary to establish a lignin-based biorefinery paradigm for value-added application of lignin. Furthermore, opportunities and challenges in current lignin biorefinery were proposed to evaluate the feasibility of lignin-based biorefinery model. In summary, it is believed that the NMR methodology for illuminating the structural characteristics and chemical reactivity of lignin polymers will maximize the ultimate utilization of lignin in the biorefinery process, such as developing lignin-based materials and chemicals.